Microwave drying of spice and herbs
- How does it work?
- What can it be used for?
- What can it not be used for?
- Related Facilities
- Further Information
|Key words||Spice, herbs, microwave, drying, dehydration, heat sensitive compound, volatile|
How does it work?
|Primary objective||Drying of spices and other biological material like herbs without decrease of volatile and heat sensitive compounds, thus reach high quality food (better nutritional value, colour, taste).|
|Working principle|| Using microwave heating [link to DS microwave heating], the energy is transferred to the wet matter with higher efficiency and the moisture is removed faster. This makes that the drying process takes less time and energy . The equipment can be arranged as batch or continuous. The bed should be mixed or rotating. The number of magnetrons depends on conformation and required power level .
The microwave heating can be combined with vacuum. [2, 3, 4]
|Additional effects||Fast start up and shut down procedures.|
|Important process parameters||The properties (like cavity design, power) of microwave drying equipment depend on the raw material (moisture - water activity, structure, origin). We can adjust the power of microwave; structure, size and shape of dried material . See DS Microwave heating|
|Important product parameters||Moisture - water activity, structure, origin.|
What can it be used for?
|Products||All bio-materials can be dried using microwaves. For spices, herbs and other low volume material with highly sensitive components (aromatic, medicinal, colour) microwave drying is especially convenient.|
|Operations||Drying, heating of bio-material. See DS Microwave heating.|
|Solutions for short comings|| Need of speeding up the drying process and to reduce losses of volatile compounds as much as possible.
During conventional hot-air drying, some parts of the material can be overheated, leading to decomposition of the heat sensitive compounds or evaporation of the volatile compounds .
What can it NOT be used for?
|Products||Metal containing materials.|
|Operations||Like with classical drying. E.g. too much water is better to separate otherwise.|
|Other limitations||Incorrect conditions can cause colour changes (browning). Should be tested for each product or group of products.|
|Risks or hazards||Strong electromagnetic field. See DS Microwave heating|
|Maturity||Microwave heating is a technology commonly used in industry and also in household. Vacuum drying is commonly used too.|
|Modularity /Implementation|| Microwave draying replaces other drying techniques. No special changes required.
Other special conditions like vacuum, combination with convective heating can be added. [4, 5]
|Consumer aspects||No problems expected. Consumers use microwave ovens at home. Moreover this technology results in spices with better properties (colour, flavour, microbiological safety…).|
|Legal aspects|| No special aspects comparing with microwave heating.
See DS Microwave heating.
|Environmental aspects||This technology is environmentally friendly. The efficiency of energy transfer is much higher, than for other heating techniques.|
Facilities that might be interesting for you
|Institutes||University of Saskatchewan, Universidad Miguel Hernández, Wrocław University of Environmental and Life Sciences, Wageningen UR - FBR|
|References||  Shaw, M.; Meda, V.; Tabil, L. Jr.; Opoku, A Drying and color characteristics of coriander foliage using convective thin-layer and microwave drying. J Microw Power Electromagn Energy 2007, 41 (2), 59-68.
 Calín-Sáncheza, Á.; Szumnyb, A.; Figielc, A.; Jałoszyńskic, K.; Adamskid, M.; Carbonell-Barrachinaa, Á. A. Effects of vacuum level and microwave power on rosemary volatile composition during vacuum–microwave drying. Journal of Food Engineering 2011, 103 (2), 219-227
 Orsat, V.; Yang, W.; Changrue, V.; Raghavan, G. S. V. Microwave-Assisted Drying of Biomaterials. Food and Bioproducts Processing 2007, 85 (3), 255-263
 Figiel, A. Drying kinetics and quality of vacuum-microwave dehydrated garlic cloves and slices. Journal of Food Engineering 2009, 94 (1), 98-104
 Sharma, G. P.; Prasad, S. Specific energy consumption in microwave drying of garlic cloves. Energy 2006, 31 (12), 1921-1926
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